174 Dr. R. Greeff on Autolytus prolifer, 
satisfactorily account for the observations previously made by 
Quatrefages upon the latter*. A further step in the natural 
history of Autolytus was furnished by Max Miillert in his 
excellent observations on Sacconereis helgolandica, although 
the genetic connexion between Sacconerers and Autolytus re- 
mained unknown to him. It was again Krohn} who correctly 
recognized and established the connexion between these two 
animals, and showed that the male and female individuals of 
Sacconerets helgolandica observed by Max Miiller were merely 
the freed male and female buds of Autolytus prolifer. In the 
same year (1855), and independently of Max Miiller’s state- 
ments, P. H. Gosse§ also described Sacconerets, and indeed 
its male form, to which that observer gives the new name of 
Crithida thalassina. 
For a very detailed memoir, published in the year 1862, 
upon the natural history and, especially, the sexual relations 
and development of Awtolytus, we are indebted to Agassiz||, 
who, however, on the whole only carried further the notions 
already expressed by Krohn, especially with regard to the 
connexion between Autolytus and Sacconereis, but also proved 
that the genus Polybostrichus, founded in 1843 by Cirsted{], is 
likewise only a male bud of Awtolytus, and therefore identical 
with the male Sacconereis helgolandica of M. Miiller** and 
with Crithida thalassina of Gosse. Agassiz, moreover, was the 
first who observed the brood of the sexual buds of Awtolytus. 
and their development into the primary individuals, and thus 
filled up what had previously been an important gap. Never- 
theless, notwithstanding the great amount of material pre- 
sented by him, he still remains im many respects behind Krohn 
as regards the accuracy and clearness of his observations. The 
generic characters so distinctly pointed out by Krohn for Aw- 
tolytus especially have not been duly noticed by Agassiz: thus, 
for example, the characteristic elegant circlet of little pointed. 
teeth which crowns the entrance into the tortuous cesophagus is 
* Comptes Rendus, August 1843, and Annales des Sci. Nat. 1844, 
tome i. p. 22. See also the subsequent more detailed treatise upon Syllis 
prolifera, “ Mémoire sur la Génération alternante des Sys,” in Ann. Sci. 
Nat. sér. 4. tome ii. p. 143, pl. 4. : . 
+ Miiller’s Archiv, 1855, p. 18, pls. 2 & 3. { Ibid. 1855, p. 489. 
§ Ann. & Mag. Nat. Hist. ser. 2. vol. xvi. p. 305, pl. 8. fig. 5. | 
|| “On Alternate Generation in Annelids, and the Embryol of 
Autolytus cornius,” Boston Journ. Nat. Hist. vol. vii. p. 384, pls. 9, 10, 
& 11. | 
q Gronland’s Annulata Dorsibranchiata, p. 30, pl. 5. fig. 62. Copen- 
hagen, 1843. ; 
** The identity of Sacconereis and Polybostrichus was indicated in the 
same year, and apparently before Agassiz, by Keferstein, ‘ Zeitschr. fiir 
wiss. Zool. Bd. xii. p. 113, pl. 11. figs. 1-6. 
